Abstract: The mountainous region of southwestern China is characterized by complex geological structures, where significant variations in lithology and stratum attitudes within the same slope section are frequently encountered. This study aims to investigate the differences in stability and failure mechanisms between soft-rock and hard-rock bedding slopes under varying bedding dip angles, thereby enabling the development of targeted engineering protection measures. Taking the left-side bedding slope along the ZK21+120～ZK21+770 section of the Bilong expressway in Guizhou Province as an example, the research conducted a comparative numerical analysis using Phase2 software. The modeling incorporated data from engineering surveys, geological mapping, borehole drilling, and laboratory testing for both silty mudstone (representing soft rock) and limestone (representing hard rock). The results indicate that slope stability is poorest and deformation is greatest when the bedding dip angle is around 35°. Failure modes vary with dip angle: silty mudstone slopes exhibit four distinct failure modes: sliding-tension cracking, bedding-plane sliding, sliding-bending, and compression-bending; whereas limestone slopes display three failure modes: sliding-tension cracking, bedding-plane sliding, and compression-bending. Significant differences exists between soft-rock and hard-rock bedding slopes in terms of stability and deformation–failure characteristics, leading to different engineering protection priorities. Therefore, for bedding slopes, a bedding dip angle of approximately 50° serves as a critical threshold. For gently dipping slopes (<50°), toe support should be the primary measure, supplemented by surface anchoring. For steeply dipping slopes (>50°), surface anchoring should be prioritized, with toe support playing a secondary role.